The proposed research examines the effects of temperature and pressure on the phase transitions and morphology of blood platelets and their microtubules. In addition, examination of the viable life time of platelets stored under various conditions with the goal of lengthening the viable storage life of blood platelet concentrates will be made. Cooling is known to disaggregate the microtubules in platelets, and platelets lose their discoidal shape assuming a more random, irregular shape with numerous pseudopods. Preliminary work has shown that the application of 2500 to 9000 psi of pressure prevents this shape change on cooling. This project will examine the fundamental processes involved in these changes including study of the microtubules, suspensions of contractile protein and intact platelets under varying conditions of pressure and temperature. The feasibility of using pressure accompanied by temperature to prolong the viable storage life of blood platelets will be examined using both in vitro and in vivo (animal) techniques such as hypotonic shock, platelet aggregation and 51 Chromium labeling. The use of some chemical substances such as PGE1, ATP, and gentisic acid will be considered. Additionally, fundamental information on the effects of pressure on microtubules and hydrophobic bonding should be obtained.